Cryptology ePrint Archive: Report 2005/291

Abstract: We initiate the study of two-party cryptographic primitives with unconditional security, assuming that the adversary's {\em quantum}memory is of bounded size. We show that oblivious transfer and bit
commitment can be implemented in this model using protocols where honest parties need no quantum memory, whereas an adversarial player needs quantum memory of size at least $n/2$ in order to break the protocol, where $n$ is the number of qubits transmitted. This is in sharp contrast to the classical bounded-memory model, where we can only tolerate adversaries with memory of size quadratic in honest players' memory size. Our protocols are efficient, non-interactive and can be implemented using today's technology. On the technical side, a new entropic uncertainty relation involving min-entropy is established.